1. Field of the Invention
The present invention relates to a stop valve which is adapted to be employed for a gas storage container or interposed in a midway position of a piping and, more particularly, to a technique to prevent a fluid leakage caused by an accidental opening of a stop valve of which handle would be turned by other objects brought into contact therewith or by a mistaken manipulation thereof.
2. Description of the Prior Art
For such a kind of stop valve, the basic construction thereof is disclosed in Japanese Laid-Open Patent Publication No. 1987-258276 which was formerly proposed by the inventors of the present invention.
As shown in FIGS. 9 and 10, the basic construction is as follows.
When a handle 107 of a stop valve 102 is turned in the valve closing direction thereof, a thrust threaded member 125 is adapted to be advanced like a screw relative to a valve box 109 and a valve body 114 is adapted to be moved toward the valve closing side by a thrust imparted thereby 125 so that a valve body sealing surface 114a can be brought into contact with a valve seat 110a to attain a valve closing. The handle 107 is fitted to the input portion 125a of the thrust threaded member 125 so as to transmit a turning force thereto 125 as well as to be detachable in the axial direction thereof 125. There are provided at least coned disc springs S' and an intermediate transmission member 126 in order within a valve closing thrust transmission mechanism T' arranged from the thrust threaded member 125 to the valve body 114 so that the intermediate transmission member 126 can be urged in the valve closing direction by means of the coned disc springs S' under a condition capable of being advanced and returned within a predetermined extent in the valve opening and closing directions relative to the thrust threaded member 125.
A restraining means 142 for stoppers 141 for the handle 107 is formed along both the thrust threaded member 125 and the intermediate transmission member 126. This restraining means 142 is so constructed as to be changed over between a handle holding condition A' wherein the stopper 141 is restrained in a stopping engagement position X' with respect to the handle 107 and a handle releasing condition B' wherein the restraint against the stopper 129 is released.
Under such a condition that the intermediate transmission member 126 has been advanced toward the valve closing side by means of the coned disc springs S' relative to the thrust threaded member 125, the restraining means 142 is adapted to be brought into the handle holding condition A'.
To the contrary, under such a condition that the thrust threaded member 125 has been advanced toward the valve closing side against the coned disc springs S' relative to the intermediate transmission member 126, the restraining means 142 is adapted to be brought into the handle releasing condition B'.
In the above-mentioned basic construction, a construction of the portion for transmitting a thrust from the thrust threaded member 125 to the valve body 114 through the intermediate transmission member 126 is as follows, as shown in FIGS. 9 and 10.
That is, an output portion 125b of the thrust threaded member 125, the coned disc springs S' and an input portion 126a of the intermediate transmission member 126 are arranged in series so that the whole thrust imparted by the thrust threaded member 125 can be transmitted to the valve body 114 through the coned disc springs S' and the intermediate transmission member 126 in order.
In the above-mentioned conventional construction, the valve closing manipulation for the stop valve 102 is carried out as follows.
When the handle 107 is manipulated so as to be turned in the valve closing direction from the valve-opened state shown by solid lines in FIGS. 9 and 10, the thrust threaded member 125 is advanced like a screw so that the valve body 114 can be moved toward the valve seat 110a through the coned disc springs S' and the intermediate transmission member 126. During the enhancement of the contact pressure between the valve body sealing surface 114a of the valve body 114 and the valve seat 110a after they have been brought into contact with each other, the intermediate transmission member 126 is received by the valve seat 110a through the valve body 114 and meantime the thrust threaded member 125 is further advanced so that the coned disc spring S' are compressed. And when the coned disc springs S' have been compressed completely, the thrust threaded member 125 is received by the intermediate transmission member 126 through the coned disc springs S' which have been made undeformable any more and the handle 107 becomes unturnable abruptly. An operator feels that unturnable state by a heavy resistance thereof and then finishes the valve closing manipulation of the handle 107. In this valve-closed state, the thrust threaded member 125 is advanced toward the valve closing side relative to the intermediate transmission member 126 so that the restraining means 142 can be opened and changed over to the handle releasing condition B' (refer to a figure indicated by an alternate long and two short dashes line in FIG. 10). Whereby, the handle 107 can be pulled off from the thrust threaded member 125 by merely lifting it 107 up (refer to a figure by an alternate long and short dash line in FIG. 10).
However, since the conventional construction of the stop valve is used as mentioned above, there are following problems associated therewith.
Since the coned disc springs S' are compressed completely at the time of the valve closing manipulation, they are apt to cause creep deformations due to a multiplicity of repetitions of the valve closing manipulation. In the case of such creep deformations of the coned disc springs S', the handle 107 can be manipulated for the valve closing by a small force as well as the thrust threaded member 125 can be advanced readily toward the valve closing side relative to the intermediate transmission member 126 so that the restraining means 142 is changed over to the handle releasing condition B'. Therefore, in spite of the incompletion of the valve closing manipulation, the handle 107 is allowed to be pulled off. Resultantly, a contact force provided for a sealing between the valve body sealing surface 114a and the valve seat 110a becomes insufficient and a leak of fluid is caused.
Further, when the stop valve 102 is subjected to a vibration in its valve closed state, an engaged threaded portion of the thrust threaded member 125 is apt to be loosened due to the creep deformations of the coned disc springs S'. Thereby also, a leak of fluid is caused.